docs: def _compute_distance(self, rup, dists, C):
          """
          equation 3 pag 1960:
  
          ``c31 * logR + c32 * (R-Rref)``
          """
          rref = 1.0
          c31 = -1.7
          return (c31 * np.log10(dists.rhypo) + C['c32'] * (dists.rhypo - rref))